Lab Manual Elements of Mechanical Engineering ( )

Transcription

1 Lab Manual Elements of Mechanical Engineering ( ) Darshan Institute of Engineering and Technology, Rajkot.

2 Darshan Institute of Engineering & Technology Certificate This is to certify that Mr./Ms. Enrollment No. Branch Semester 1 st & 2 nd has satisfactory completed the course in the subject Elements of Mechanical Engineering in this institute. Date of Submission: - / / Staff in Charge Head of Department

3 DARSHAN INSTITUTE OF ENGG. & TECH. B.E. Semester I Elements of Mechanical Engineering( ) List of Experiments Sr. No. Title Date of Performance Date of submission Sign Marks (Out of10) 1 To understand construction and working of various types of boilers. 2 To learn about various Boiler Mountings & Accessories. 3 To understand construction and working of I. C. Engines. 4 To study about engine performance parameters. 5 To understand construction and working of different types of pumps. 6 To understand construction and working of different types of air compressors. 7 Demonstration of domestic refrigerator. 8 To understand construction, working and applications of different types of coupling, clutch and brake. 9 Demonstration of various types of power transmission elements.

4 EXPERIMENT-1 Objective To understand construction and working of various types of boilers 1.1 Introduction Steam boiler may be defined as A closed pressure vessel in which steam is generated with capacity exceeding 25 liters gauge pressure greater than or equal to 1 kg/cm 2, and water Is heated at 100 C or above. The steam produced may be supplied: 1) For generating power in steam Engine or steam turbines. 2) At low pressures for industrial process work in cotton mills, sugar factories, etc. 3) For producing hot water for supply of hot water and for heating the buildings in cold weather. 1.2 Classification of Steam Boilers According to relative position of water and hot gases. Fire Tube boiler - hot gases pass through fire tubes which are surrounded by water Water tube - water flows inside the tubes and the hot flue gases flow outside the tubes According to the axis of the shell Vertical boiler the axis of the shell is vertical. Horizontal boiler the axis of the shell is horizontal Inclined boiler the axis of the boilers is inclined According to the method of firing Externally fired boilers furnace is located outside the shell. Internally fired boilers furnace is located inside the shell, means combustion takes place inside the boiler shell According to the Method of Water circulation Forced Circulation boilers - water is circulated by pumps which is driven by motor and Natural Circulation boilers - water is circulated by natural convection currents which are set up due to the temperature difference produced by the application of heat According to the Pressure of steam High pressure boilers working pressure is more than 25 bars. Example: Babcock and Wilcox boiler Medium pressure boilers working pressure is 10 to 25 bars. Example: Lancashire and locomotive boiler Low pressure boilers working pressure is 3.5 to 10 bars. Example: Cochran and Cornish boiler According to the mobility of boiler Stationary boilers it is used for stationary plants. Mobile boilers it can move from one place to another. Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 1

5 1.2.7According to the number of tubes in the boiler Single tube boilers they have only one fire or water tube. Multi tube boilers they have more than one fire or water tubes General terms (parts) used in Steam Boiler 1.3.1Cylindrical shell It is made up of steel plates bent into cylindrical form and rewetted and welded together. The ends of shell are closed by means of plates in different shapes. It should have sufficient capacity to contain water and steam Combustion chamber It is the space, generally below the boiler shell, meant for burning fuel in order to produce steam from the water contained in the shell Grate It is a platform, in the combustion chamber, upon which fuel is burnt. The grate consists of cast iron bars which are spaced apart so that air can pass through them Furnace It is a chamber formed by the space above grate and bellows the boiler shell in which combustion take place. It is also called a Fire box Fire Hole It is the hole through which coal is added to the furnace Ash Pit (ash pan) It is the area in which the ash of burnt coal is collected Smoke chamber (smoke box) The waste gases are collected here and then releases to the chimney and then to atmosphere Man Hole It is a hole provided on to the boiler shell so that a workman can go inside the boiler for inspection Hand Holes It is a hole provided on the shell to give to give east access for the purpose of cleaning the water tubes or some other internal parts of boiler Mud box It collects all impurities present in the water. It is at the bottom of the barrel or shell. These impurities are removed time to time by help of blow off cock Steam collecting pipe When the steam leaving the boiler, it contains certain amount of water.antipriming pipe is used to separate water particles from the steam and to collect dry steam from boiler. Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 2

6 Questions: (1) Explain Working of following boiler with neat sketch: a) Cochran boiler b) Babcock and Wilcox boiler c) Lancashire boiler (2) Give difference between fire tube (Cochran) and water tube (Babcock Wilcox) boiler. Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 3

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12 Objective EXPERIMENT 2 To learn about various Boiler Mountings & Accessories Mountings These are the safety devices for the safe working of steam boiler and they are mounted on the steam boiler like Water indicator valve, pressure gauge, fusible plug, etc. Accessories These devices are used for increasing the efficiency of boilers. They are integral parts of the boiler and are not mounted on the boiler. They include Super heater, Economizer, etc. 2.1 List of Boiler Mountings & Accessories According to IBR the following mountings should be fitted to the boilers 1) Two Safety valves 2) Two water level indicators 3) A pressure gauge 4) A Steam stop valve 5) A feed check valve 6) A blow off cock 7) An attachment of inspector s test gauge 8) A man hole 9) Mud holes or sight holes Commonly used boiler accessories are as 1) Feed pumps 2) Injector 3) Economizer 4) Air preheater 5) Superheater 6) Steam separator 7) Steam trap Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 9

13 Questions: (1) What are the purposes of mounting? Explain working of following with neat sketch. a) Water level indicators b) Fusible plug c) Pressure gauge d) Spring loaded safety valve e) Feed check valve (2) What are the purposes of accessories? Explain working of following with neat sketch. a) Economiser b) Super heater c) Air pre-heater Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 10

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22 EXPERIMENT - 3 Objective To understand construction and working of I. C. Engines 3.1 Introduction In 1876 four stroke engine based on Otto cycle was developed by a German engineer Nikolous Otto, Which revolutionized the development of internal combustion engines and are even used till date. Diesel engine was developed by another German engineer Rudolf Diesel in the year Engine refers to a device which transforms one form of energy into the other form. Heat engine is a modified form of engine used for transforming chemical energy of fuel into thermal energy and subsequently for producing work." Heat engines may be classified based on where the combustion of fuel takes place. i.e. whether outside the working cylinder or inside the working cylinder. (a) External Combustion Engines (E.C. Engines) (b) Internal Combustion Engines (I.C. Engines) 3.2 Comparison of I.C. Engines and E.C. Engines Sr.N0 I.C. Engine E.C. Engine 1. Combustion of fuel takes place inside the Combustion of fuel takes place cylinder. outside the cylinder 2. Working fluid may be Petrol, Diesel & Various types of gases. Working fluid is steam 3. Require less space Require large space 4. Capital cost is relatively low. Capital cost is relatively high. 5. Starting of this engine is easy & quick Starting of this engine requires time. 6. Thermal efficiency is high. Thermal Efficiency is low. 7. Power developed per unit weight of these Power Developed per unit weight of engines is high. these engines is low 8. Fuel cost is relatively high. Fuel cost is relatively low. Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 19

23 3.3 Classification of I.C. Engines I.C. Engines may be classified according to, a) Type of the fuel used as : (1) Petrol engine (2) Diesel engine (3)Gas engine (4) Bi-fuel engine (Two fuel engine) b) Nature of thermodynamic cycle as : (1) Otto cycle engine (2) Diesel cycle engine (3) Duel or mixed cycle engine c) Number of strokes per cycle as : (1) Four stroke engine (2) Two stroke engine d) Method of ignition as : (1) Spark ignition engine (S.I. engine) Mixture of air and fuel is ignited by electric spark. (2) Compression ignition engine (C.I. engine) The fuel is ignited as it comes in contact with hot compressed air. e) Method of cooling as : (1) Air cooled engine (2) Water cooled engine f) Speed of the engine as : (1) Low speed (2) Medium speed (3) High speed g) Number of cylinder as : (1) Single cylinder engine (2) Multi cylinder engine h) Position of the cylinder as : (1) Inline engines (2) V engines (3) Radial engines (4) Opposed cylinder engine (5) Opposed piston engine 3.4 Engine details The various important parts of an I.C. engine are shown in figure. Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 20

24 Cylinder It is the heart of the engine in which the fuel is burnt and the power is developed. Cylinder has to withstand very high pressure and temperature because the combustion of fuel is carried out within the cylinder. Therefore cylinder must be cooled. The inside diameter is called bore. To prevent the wearing of the cylinder block, a sleeve will be fitted tightly in the cylinder. The piston reciprocates inside the cylinder Cylinder head Cylinder head covers top end of cylinder. It provides space for valve mechanism, spark plug, fuel injector etc Piston The piston is a close fitting hollow cylindrical plunger reciprocating inside the cylinder. The power developed by the combustion of the fuel is transmitted by the piston to the crank shaft through connecting rod Piston Rings The piston rings are the metallic rings inserted into the circumferential grooves provided at the top end of the piston. These rings maintain a gas-tight joint between the piston and the cylinder while the piston is reciprocating in the cylinder Piston pin or Gudgeon pin It is the pin joining small end of the connecting rod and piston. This is made of steel by forging process Connecting Rod It is the member connecting piston through piston pin and crank shaft through crank pin. It converts the reciprocating motion of the piston into rotary motion of the crankshaft. It is made of steel by forging process Crank and Crankshaft The crank is a lever that is connected to the big end of the connecting rod by a pin joint with its other end connected rigidly to a shaft, called crankshaft. It rotates about the axis of the crank shaft and causes the connecting rod to oscillate Valves Engine has both intake and exhaust type of valves which are operated by valve operating mechanism (Refer Fig. 3.5). The valves are the device which controls the flow of the intake and the exhaust gases to and from the engine cylinder Flywheel It is a heavy wheel mounted on the crankshaft of the engine. It minimizes cyclic variation in speed by storing the energy during power stroke, and same is released during other stroke Crankcase It is the lower part of the engine, serving as an enclosure of the crankshaft and also as a sump for the lubricating oil Carburetor Carburetor is used in petrol engine for proper mixing of air and petrol. Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 21

25 Fuel pump Fuel pump is used in diesel engine for increasing pressure and controlling the quantity of fuel supplied to the injector Fuel injector Fuel injector is used to inject diesel fuel in the form of fine atomized spray under pressure at the end of compression stroke Spark plug Spark plug is used in petrol engine to produce a high intensity spark for ignition of air fuel mixture in the cylinder. 3.5 Engine Terminologies Bore: The inner diameter of the engine cylinder is called a bore Stroke: It is the linear distance traveled by the piston when it moves from one end of the cylinder to the other end. It is equal to twice the radius of the crank Dead Centers: In the vertical engines, top most position of the piston is called Top Dead Centre (TDC). When the piston is at bottom most position, it is called Bottom Dead Centre (BDC). In horizontal engine, the extreme position of the piston near to cylinder head is called Inner Dead Centre (I.D.C.) and the extreme position of the piston near the crank is called Outer Dead Centre (O.D.C.) Clearance Volume (Vc) It is the volume contained between the piston top and cylinder head when the piston is at top or inner dead centre Stroke volume (swept volume) It is volume displaced by the piston in one stroke is known as stroke volume or swept volume. Let, Vs = stroke volume, L = stroke length, d = Bore = Compression Ratio The ratio of total cylinder volume to clearance volume is called the compression ratio (r) of the engine. Total cylinder volume = Vc + Vs Compression Ratio, = = + For petrol engine r varies from 6 to 10 and for Diesel engine r varies from 14 to 20. Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 22

26 3.5.7 Piston speed It is average speed of piston. It is equal to 2LN, where N is speed of crank shaft in rev/sec. Where, L = Stroke length, m N = Speed of crank shaft, RPM, = 2 60 Questions: (1) Explain Four stroke petrol engine (Spark ignition four stroke engine OR Otto four stroke engine ) with sketch. (2) Explain working of two stroke petrol engine with diagram. (3) Explain working of four stroke diesel engine (compression ignition engine ) with sketch. (4) Give difference between petrol and diesel engine. Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 23

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33 Objective EXPERIMENT - 4 To study about engine performance parameters 4.1 Indicated power The power produced inside the engine cylinder by burning of fuel is known as Indicated power (I.P.) of engine. It is calculated by finding the actual mean effective pressure. Where, a = Area of the actual indicator diagram, cm 2 l = Base width of the indicator diagram, cm s = spring value of the spring used in the indicator, N/m 2 /cm Indicated power of a Four-stroke engine Let, Pm = Mean effective pressure, N/m 2 L = Length of stroke, m A = Area of cross section of the cylinder, m 2 N = RPM of the engine crank shaft n = Number of power strokes per minute Work produced by the engine per cycle,, = = [Mean force acting on the piston] X [Piston displacement in one stroke] Work produced by the engine per minute,. = [Work produced by the piston per cycle] X [Number of power stroke per minute] In four-stroke I.C. engines, number of power stroke per minute will be equal to half of RPM because we get one power stroke in two revolutions of the crank shaft. i.e. = 2 Work produced by the engine per minute, 2 (.. ) = 60 2 Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 30

34 .. = Indicated power of a two stroke I.C. engine In two stroke I.C. engine, the number of power strokes per minute will be equal to RPM of crank shaft i.e. n = N Indicated power of a two stroke I.C. engine is given by.. = Brake Power (B.P.) It is the power available at engine crank shaft for doing useful work. It is also known as engine output power. It is measured by dynamometer. It can be calculated as follows: Let, W = Net load acting on the brake drum, N R = Radius of the brake drum, m N = RPM of the crank shaft T = Resisting torque, Nm Pmb = Brake mean effective pressure And =.. = = The piston connecting rod and crank are mechanical parts, moving relative to each other. They offer resistance due to friction. Therefore a certain fraction of power is lost due to friction of the moving parts. The amount of the power lost in friction is called friction power. The friction power is the difference between the I.P. and B.P. = Efficiencies Mechanical efficiency: It is defined as the ratio of the brake power and the indicated power. Mechanical efficiency is indicator of losses due to friction. = Thermal efficiency: It is the efficiency of conversion of the heat energy produced by the actual combustion of the fuel into the power output of the engine. It is the ratio of work done to heat supplied by fuel. i)indicated thermal efficiency = Indicated Power/ Heat supplied by fuel Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 31

35 .. = Where, mf = mass of fuel supplied, Kg/sec and CV = calorific value of fuel, J/kg ii) Brake thermal efficiency = Brake Power/ Heat supplied by fuel.. = Also = Relative efficiency: It is the ratio of indicated thermal efficiency of an engine to air standard cycle efficiency Air standard efficiency: It is the efficiency of the thermodynamic cycle of the engine. For petrol engine, For diesel engine, = = 1 1 ( ) = 1 1 ( ) 1 ( 1) Volumetric efficiency: It is the ratio of the volume of charge/air actually sucked at atmospheric condition to swept volume of engine. It indicates breathing capacity of the engine. = h Specific output: The specific output of the engine is defined as the power output per unit area. = Specific fuel consumption: Specific fuel consumption (SFC) is defined as the amount of fuel consumed by an engine for one unit of power production. SFC is used to express the fuel efficiency of an I.C. engine. Where, =.. h mf = Mass of fuel consumed in kg/hr and B.P. = Power produced in KW Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 32

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37 EXPERIMENT-5 Objective To understand construction and working of different types of pumps 5.1 Centrifugal Pumps A pump which employs centrifugal force for conveying liquid from one place to another is called centrifugal pump. The centrifugal pumps are of roto dynamic type pump. Types of centrifugal pump (A) According to type of casing, a. Volute or spiral casing type pump b. Vortex or whirlpool chamber type pump c. Diffuser type (casing with guide blades) pump (B) According to number of stages, a. Single stage b. Multi-stage Impeller in series Impeller in parallel 5.2 Rotary pumps Rotary pumps are positive displacement pumps. It consists of fixed casing with a rotor which may be in the form of gears, vanes, lobes, screws, cams etc. Centrifugal pump operates on principle of centrifugal action of rotation; the pressure is developed by the centrifugal action of liquid while rotary pumps the pressure is developed by positive displacement of the liquid. Rotary pump is suitable for pumping viscous fluids like vegetable oil, lubricating oil, alcohol, grease, tar etc. Types of rotary pumps There are main three types of rotary pumps as, a. Gear pump b. Vane pump c. Screw pump Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 34

38 Questions: (1) Explain working of single acting reciprocating pump with neat sketch. (2) Explain working principle of centrifugal pump. (3) Explain main parts of centrifugal pump with sketch. (4) Why priming is required in centrifugal pump? List methods of priming and explain any one of them. Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 35

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44 EXPERIMENT 6 Objective To understand construction and working of different types of air compressors 6.1 Introduction The machines which take in air or any other gas at low pressure and compress it to high pressure are called compressors. Compressors are driven by electric motors, I.C. engines gas turbines. 6.2 Classification of Compressor 1) According to method of compression Reciprocating compressor Rotary Compressor Centrifugal compressor (2) According to delivery pressure Low pressure - up to 1.1 bar Medium pressure to 8 bar High pressure 8 to 10 bar Very high pressure - above 10bar (3) According to principle of operation Positive displacement Rotodynamic or steady flow compressor (4) According to the number of stages Single stage compressor Multistage compressor (5) According to number of cylinder Single cylinder Multi cylinder (6) According the pressure limit Fans - pressure ratio 1 to 1.1 Blowers - pressure ratio 1.1 to 2.5 Compressor - pressure ratio above 2.5 (7) According to volume of air delivered Low capacity - volume flow rate up to 10 m3/min Medium capacity - volume flow rate 10 m3/min to 300 m3/min High capacity: Volume flow rate above 300 m3/min. (8) According to fluid to be compressed Air compressor Gas compressor Vapour compressor Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 41

45 Questions: (1) What is air compressor? Give application of compressed air. (2) Explain operation of reciprocating compressor without clearance. (3) Explain concept of multistage reciprocating compressor. (4) Explain Vane compressor with sketch. Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 42

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50 Objective EXPERIMENT 7 Demonstration of domestic refrigerator 7.1 Introduction Refrigeration can be defined as the method of reducing the temperature of a system below surrounding temperature and maintaining it at the lower temperature by continuously abstracting the heat from it. Refrigerator is a device which removes heat from cold body and reject to hot body (surrounding) and maintains low temperature for useful purpose. In this device, external work is required to convey heat from cold body to hot body. Refrigerant is a heat carrying medium which absorbs heat from space (desired to cool) and rejects heat to outside the refrigerator (in atmosphere). 7.2 Unit of Refrigeration It is defined as "refrigerating effect produced by melting of 1 ton of ice from and at 0 C in 24 hours." OR Amount of heat required to be removed in order to form one ton of ice in 24 hours from water at temperature 0 o C. 7.3 Coefficient of Performance It is defined as the ratio of refrigerating effect to work required for compressing the refrigerant in the compressor. It is the reciprocal of the efficiency of a heat engine. Thus the value of COP is always greater than unity. 7.4 Domestic Refrigerator The refrigerator is usually specified in terms of volumetric capacity of inside cooling space. Examples available in capacities of 65 litres, 100 litres, 165 litres, 275Iitres,1000 litres. Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 47

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52 Questions: (1) Give properties of good refrigerant. (2) Explain Vapour compression refrigeration system (VCRS) with P-H diagram. (3) Explain Vapour absorption refrigeration system with diagram. Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 49

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56 Objective EXPERIMENT-8 To understand construction, working and applications of different types of coupling, clutch and brake. 8.1 Introduction Coupling and clutches are power transmission elements. It is used for transmitting power from one shaft to the other shaft. A coupling is a device used to connect or couple two shafts while clutch is device which facilitate engage and disengage of driving shaft and driven shaft whenever required even it may rotate. The brake is frictional device whose primary function is to control the motion of machine member. It is used to bring machine member into rest or slow down. 8.2Couplings Shafts are mostly available up to 7 meter length due to transport difficulty. To get a greater length, it is necessary to joint two or more pieces of the shaft using coupling. Purposes of Coupling used are, 1. To connect shafts of motor and generator which are manufactured separately and to provide for disconnection for repairs. 2. To reduce the transmission of shock loads from one shaft to another. 3. To allow misalignment of the shaft or to introduce mechanical flexibility. 4. To introduce protection against overloads Types of couplings Couplings are divided into two main groups as follows, Rigid coupling It is used to connect two shafts which are perfectly in axial alignment. These couplings do not allow any relative rotation between the two shafts. There are basic three types of rigid coupling as follows, a. Sleeve or muff coupling b. Clamp or split muff or compression coupling c. Flange coupling: - (1) Unprotected type (2) protected type Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 53

57 8.3 Clutches The clutch is a mechanical device used to connect or disconnect from the driving shaft at wheel of the operator while power is transmitted from driving to driven shaft. In automobiles, where vehicle can be stopped for a while or to change the gear, requirement is that the driven shaft should stop but the engine should run naturally under the no load condition. This is achieved by using clutch mounted between engine shaft and gearbox shaft and which is operated by a lever. Classification of Clutch a) Friction Clutch - 1) Single plate clutch 2) Multi plate clutch 3) Cone clutch 4) Centrifugal clutch b) Positive Contact -1) Jaw clutch 8.4 Brakes Brake is a device by means of which an artificial frictional resistance is applied to a moving body in order to retard or stop the motion of a body. Clutches and brakes work on the same principle of friction but the functional difference between clutch and brake is that the clutch connects one moving part to another moving part, whereas the brake connects one moving part to another stationary part. During braking process, the brake absorbs either kinetic energy or potential energy or both by an object. In automobiles brake absorbs kinetic energy of moving vehicles. In case of elevators and hoists brake absorb potential energy released by the objects during braking period. The energy absorbed by the brake is converted in the form of heat which is dissipated to the surrounding air or water which is circulated through the passage in the brake drum. Classification of brake a) Block or Shoe brake 1) Single block brake 2 ) Double block brake b) Band brake 1) Simple band brake 2) Differential band brake c) Internal expanding shoe brake d) Disc brake Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 54

58 Questions: (1) Give classification of coupling. Explain Oldham s coupling with sketch. (2) Explain Single plate clutch (Disc clutch). (3) Explain Internal expanding shoe brake with sketch. (4) Give the difference between clutch and brake. (5) Explain working of Centrifugal clutch. Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 55

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63 Objective EXPERIMENT 9 Demonstration of various types of power transmission elements 9.1 Gear drive and friction drive In case of rope and belt drives we have seen that the velocity ratio transmitted cannot be exact due to the slip of rope or belt on the pulley. Also due to frictional losses the efficiency of power transmission in such drives is less. The power may be transmitted from one shaft to another by means of mating gears with high transmission efficiency. In early days, friction discs as shown in figure 10.1 were used for transmitting the power from one shaft to another shaft. In such a case, the power transmission capacity depends on friction between surfaces of two discs. Therefore, this method is not suitable for transmitting higher power as slip occurs between the discs. (a) Frictional disc (b) Gear drive In order to transmit a definite power from one shaft to another shaft to the projection on one disc and recesses on another disc can be made which can mesh with each other. This leads to the formation of teeth on both discs and the discs with teeth on their periphery are known as "Gears". Advantages 1. It is a positive drive (no slip) i.e. it transmits exact velocity ratio from one shaft to another shaft. 2. It can transmit very large power. 3. High transmission efficiency. 4. Requires less space. 5. Reliable. Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 60

64 Disadvantages 1. Manufacturing cost of gear is high, since special tools and machinery is required for gear manufacturing. 2. Maintenance cost of gear drive is also high due to lubrication requirements. 3. The error in cutting teeth may cause vibrations and noise during operation. 4. It requires precise alignment of shafts. Spur gear Use When the axis of two shafts are parallel to each other. These gears have teeth parallel to the axis of the shaft. Helical gear In helical gears the teeth are at some angle called helix angle with respect to axis of the shaft. Advantages 1. It runs quieter as compared to spur gears since the contact between teeth is gradual. 2. Transmission of load is gradual which results in low impact stresses and reduction in noise. Thus they are used for high speed transmission. Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 61

65 Disadvantage They induce axial thrust in one direction on the bearings. Rack and pinion It is a special case of spur gear in which one gear is having infinite diameter called "Rack". Use To transmit the rotary motion into reciprocating motion or vice-versa. Application Lathe machine, drilling machine and measuring instrument. Bevel gear Use When power is required to be transmitted from one shaft to another shaft which are intersecting to each other then bevel gears are used. Generally, the angle between two shafts is 90⁰. The bevel gears are of two types, 1. Straight bevel gear 2. Spiral bevel gear Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 62

66 (1) Straight bevel gears In straight bevel gears the teeth are formed straight on the cones, and they are parallel to the axis of the gear. (2) Spiral bevel gears In a spiral bevel gear, the teeth are formed at an angle with respect to its axis. The contact between two meshing teeth is gradual and smooth from start to end, as in case of helical gears. Application Automobile differential Spiral Gears (Skew gears or Crossed helical gears) Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 63

67 Use To transmit power from one shaft to another shaft which are non parallel and non intersecting. For low load transmission only since they have point contact between mating teeth. Worm and worm wheel Use To transmit power from one shaft to another shaft which are non intersecting and their axes are normally at right angles to each other. Application Lathe machine to get large speed reduction. Questions: (1) What is belt drive? Explain types of belt drive with sketch. (2) Give comparison between individual drive and group drive. (3) Give classification of gear and explain any three with sketch. (4) Give comparison between belt drive, chain drive and gear drive. Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 64

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73 Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 70

74 Conclusion: Sign Date Elements of Mechanical Engineering ( ) Darshan Institute of Engineering & Technology Page 71

75 C 1. Properties of Gases An air vessel contains 9 kg of air at initial pressure and temperature are 6 bar and 20 C respectively. After heat supplied pressure of air becomes 12 bar. Take value of characteristic gas constant is KJ/kg K and C v = KJ/kg K. Determine 1. Final temperature 2. Heat supplied 3. Work done during process 4. Change in internal energy 5. Change in enthalpy. ANSWERS: [1] T 2 = 586 K [2] Q = KJ [3] W = 0 KJ [4] U = KJ [5] H = KJ T 1. One kg of air at 450 kpa and occupying 0.25m 3 is heated at constant volume until the temperature has risen to 270 C. Determine (i) initial te mperature of air, (ii) final pressure, (iii) heat supplied, (iv) change in internal energy per kg and (v) change in enthalpy during process. Take C p = kj/kg-k and C v = kj/kg-k. ANSWERS: [1] K [2] 6.4 bar [3] KJ [4] KJ/kg [5] KJ H 1. In a vessel 9 kg of air is heated with non-flow, constant volume process that pressure of air is increased two times that of the initial value. The initial temperature is 20 C. Calculate 1. Final temperature 2. Change in internal energy 3. Change in enthalpy and 4. Heat transfer 5. Work done Take R=0.287 KJ/kg K. and C v =0.718 KJ/kg K for air. ANSWERS: [1] 586 K [2] KJ [3] KJ [4] KJ [5] 0 KJ C 2. A tank filled with 1 kg of gas at initial pressure and volume are 5 bar and 0.20 m 3, respectively. If 47 KJ heat addition to the gas then its temperature reaches 127 C. Take value of characteristic gas constant is 300 Nm/kg K and C p = KJ/kg K. Determine 1.Work done during process 2. Initial temperature 3. Change in internal energy 4. Change in enthalpy 5. Final volume. ANSWERS: [1] W = 0 KJ [2] T 1 = K [3] U = KJ [4] H = KJ [5] V 2 = 0.20 m 3 T 2. A cylinder vessel of 1 m diameter and 4 m length has hydrogen has at pressure of 100 Kpa and 27 C Determine amount of heat to be supplied so as to increased pressure to 125 Kpa. For hydrogen C p = KJ/kg K and C v = KJ/kg K. ANSWER: Q = KJ H 2. A tank contains 3m 3 of air at 25 bar absolute pressure. This air is cooled until its pressure and temperature decrease to 15 bar and 21 C respectively. Determine change in internal energy, change in enthalpy and heat transfer. Take C p = kj/kg-k and C v = kj/kg-k for air. ANSWERS: [1] KJ [2] KJ [3] KJ

76 C 3. T 3. H 3. C 4. T 4. 5 kg of gas contains in piston cylinder assembly with initial volume, pressure and temperature are 0.5 m 3, 8 bar and 105 C respectively. If heating of gas at constant pressure then its temperature becomes 270 C. Assume value of C p = KJ/kg K and C v = KJ/kg K. Determine 1.Heat supplied during process 2. Final volume 3. Work done 4. Change in internal energy 5. Change in enthalpy 6. Final pressure. ANSWERS: [1] Q = KJ [2] V 2 = m 3 [3] W = KJ [4] U = KJ [5] P 2 = 8 bar The cylinder contains gas with initial pressure, volume, and temperatures are 0.7 Mpa, 0.14 m 3, and 15.5 C respectively. The volume of gas increases up to 0.5 m 3 after heat added at constant pressure. Assume value of characteristic gas constant is 287 J/k g K and C v = KJ/kg K. Determine 1.Final temperature, Final pressure 2. Heat supplied during process 3. Work done 4. Change in enthalpy. ANSWERS: [1] T 2 = K, P 2 = 700 KN/m 2 [2] Q = KJ [3] W = 252 KJ [4] H = KJ The gas whose pressure, volume, and temperatures are 2.75 bar, 0.09 m 3, and 185 C respectively has the state changed at constant pressure until its temperature becomes 15 C. Take R= 0.29 KJ/kgK and C p = KJ/kg K. Calculate 1. Heat transferred 2. Work done during the process. ANSWERS:[1] Q = KJ [2] w = KJ In an air compressor air enters with initial volume, pressure and temperatures are m 3, 0.3 bar and 95 C respectively. If compression occurs isothermally then pressure after compression raises up to 0.1 MPa. Assume value of characteristic gas constant is 287 J/kg K. Determine 1.Mass of air 2. Final temperature 3. Heat supplied during process 4. Work done 5. Change in internal energy 6. Change in enthalpy. ANSWERS: [1] m = kg [2] T 2 = 368 K [3] Q = KJ [4] W = KJ [5] U = 0 KJ [6] H = 0 KJ 0.45 kg of air is sucks in an air compressor with initial pressure and temperature are 20 kn/m 2 and 30 C respectively. If compression is isothermal then volume after compression reduces up to 0.06 m 3. Assume value of characteristic gas constant is 287 J/kg K.determine 1.Final temperature 2. Init ial volume 3. Work done 4. Heat supplied during process 5. Change in enthalpy and 6. Change in internal energy. ANSWERS: [1] T 2 = 303 K [2] V 1 = m 3 [3] W = KJ [4] Q = KJ [5] U = 0 KJ [6] H = 0 KJ

77 H 4. In an air compressor air enters at bar and 27 C having volume 5 m 3 /kg and it is compressed to 12 bar isothermally. Determine 1. Work done 2. Heat transfer and 3. Change in internal energy. ANSWERS: [1] W = KJ [2] KJ [3] U = 0 KJ C 5. Determine the work done in compressing one kg of air from a volume of 0.15 m 3 at a pressure of 1 bar to a volume of 0.05 m 3, when the compression is (i) isothermal and (ii) adiabatic, take γ = 1.4. Also comment on your answer. ANSWERS: [1] W = KJ [2] w = KJ T 5. H 5. One kg of gas at 100 KN/m 2 and 17 C is compressed isothermally to a pressure of 2500 KN/m 2 in a cylinder. The characteristic equation of gas is given by the equation PV= 260T/kg where T is in degree Kelvin. Find out 1. Final temperature 2. Final volume 3. Compression ratio 4. Change in enthalpy 5. Work done on the gas. ANSWERS: [1] T 2 = 290 K [2] V 2 = m 3 [3] r = 25 [4] 0 KJ [5] KJ 0.45 kg of air at a pressure of 0.2 bar and 30 C is compressed is isothermally until its volume is 0.06 m 3. Determine the final temperature, work done & heat transferred during process, H and U. Take R=287 J/Kg K. ANSWERS: [1] 303 K [2] KJ [3] KJ [4] 0 KJ [5] 0 KJ

78 Properties of Steam C 1. T 1. H 1. C 2. T 2. Following data to be observed during test on throttling Calorimeter Pressure in main before throttling = 13 bar Pressure after throttling = 1 bar Temperature of steam after throttling = 135 C Specific heat of steam = 2.1 kj/kg K Determine dryness fraction for throttling calorimeter. ANSWER: X = On a test with throttling calorimeter, to determine dryness fraction of steam, a sample is taken from main pipe at 11 bar pressure and temperature after throttling are 1 bar and 130 C respectively. Calculate dryness fraction of steam sample. Take C p = 2.1 kj/kg K. ANSWER: X = Following data to be observed during test on throttling calorimeter Pressure in main before throttling = 6 bar Pressure after throttling = 0.1 MPa Temperature of steam after throttling = 122 C Specific heat of steam = 2.1 kj/kg K Determine dryness fraction for throttling calorimeter. ANSWER: X = Combined separating and throttling calorimeter is used to find out dryness fraction of the steam. Following readings were taken, Main Pressure = 12 bar abs. Mass of water collected in separating calorimeter = 2 kg Mass of steam condensed in throttling calorimeter = 20 kg Temperature of steam after throttling = 110 C Pressure after throttling = 1 bar abs. Assume C p of steam = 2.1 kj/kg K Calculate dryness fraction of steam. ANSWER: X = The following information is available from test of a combined separating and throttling calorimeter. Pressure of steam in a steam main = 9 bar Pressure after throttling = 1 bar Temperature after throttling = 115 C Mass of steam condensed after throttling = 1.8 kg Mass of water collected in the separator = 0.2 kg Calculate dryness fraction of steam in the main ANSWER: X =

79 H 2. C 3. T 3. H 3. C 4. Find the quality of steam supplied in a combined separating and throttling calorimeter as per below data available. Initial pressure = 10 bar Final pressure = 1 bar Water separated = 1.5 kg Steam discharged from throttling calorimeter = 20 kg Temperature of steam after throttling = 120 C ANSWER: X = Following data to be monitoring during test on combined separating throttling Calorimeter Pressure in main before throttling = 8 bar Temperature of steam after throttling = 110 C Barometer reading = 754 mm of Hg Manometer reading = 81.5 mm of Hg Mass of steam separated = 60 kg Mass of moisture (water) separated = 1.5 kg Specific heat of steam = 2.1 kj/kg K Determine dryness fraction for combined separating throttling calorimeter. ANSWER: X = Following data obtained from test on combined separating and throttling calorimeter. Pressure of steam in pipe = 7.5 bar Temperature of steam in throttling calorimeter = 110 C Pressure of steam in throttling calorimeter = 81.5 mm Hg Barometer reading = 754 mm of Hg Steam entering in to separating calorimeter = 63 kg Water collecting in separating calorimeter = 1.5 kg Calculate dryness fraction of steam entering the calorimeter. ANSWER: X = Following data to be monitoring during test on combined separating throttling Calorimeter Mass of water separated = 3.5 kg Mass of steam separated = 19 kg Temperature of steam after throttling = 107 C Pressure in main before throttling = 15 bar Barometer reading = 760 mm of Hg Manometer reading = 5 mm of Hg Determine dryness fraction for combined separating throttling calorimeter. ANSWER: X = Determine dryness fraction of steam supplied to a separating throttling calorimeter. Water separated in separating calorimeter = 0.45 kg Steam discharged from throttling calorimeter = 7 kg Steam pressure in a main pipe = 1.2 MPa Barometer reading = 760 mm of Hg

80 Manometer reading = 180 mm of Hg Temperature of steam after throttling = 140 C Take C ps of steam = 2.1 kj/kg K ANSWER: X = T 4. Following data obtained during test on combined separating and throttling calorimeter. Water separated = 2 kg Steam discharged from throttling calorimeter = 20.5 kg Temperature of steam after throttling = 110 C Initial pressure = 12 bar Barometer reading = 760 mm of Hg Final pressure = 5 mm of Hg Determine the quality of steam supplied. Take C p of superheated steam as 2.2 kj/kg K. ANSWER: X = H 4. The following data were obtained with a separating and throttling calorimeter. Pressure in pipe line = 1.6 MPa Condition after throttling = 0.1 MPa, 120 C Moisture collected in separating calorimeter during 5 minutes = 0.18 litre at 70 C Steam condensed after throttling during 5 minutes = 4 kg Determine the quality of steam in the pipeline. ANSWER: X = C 5. Following data available for 5 kg of steam at different condition. Determine 1. Enthalpy and internal energy when steam has dryness fraction 0.9 at 0.8 bar 2. Enthalpy and internal energy when steam is dry at 0.8 bar and 3. Enthalpy and internal energy when steam is superheated at 300 C at 20 bar. ANSWERS: [1] H wet = kj, U wet = kj [2] H dry = kj, U dry = kj [3] H sup = kj, U sup = kj T 5. Determine the enthalpy and internal energy of 1 kg of steam at a pressure 10 bar(abs.),(i) When dryness fraction of steam is 0.85 (ii) When steam is dry and saturated (iii) When the steam is superheated to 300 C. Neglect the volume of water and take the specific heat of superheated steam as 2.1 kj/kg K. ANSWERS: [1] H wet = kj, U wet = kj [2] H dry = KJ, U dry = kj [3] H sup = kj, U sup = kj H 5. One kg of steam at pressure of 15 bar with dryness fraction of Determine enthalpy, specific volume and internal energy of steam. ANSWERS: [1] H = kj [2] v = m 3 /kg [3] U = kj

81 Heat Engine C1. An engine working on a Carno t cycle with wo rking flu id as a gas has the max imu m pressure and temperatures of the cycle as 30 bar and 550k respectively. the expansion and compression ratios for the isothermal and adiabatic pro cesses are 4 and 6 respectively. The mass of gas in the system 1 is kg. Calculate the properties o f gas at salient po ints, the work done during the cycle and thermal efficiency. Take γ=1.4 R=0.3 KJ/kgK. ANSWERS: [V 1 = m 3 V 2 = 0.22 m 3 V 3 = 1.32 m 3 V 4 = 0.33 m 3 T 1 = 550 K T 2 = 550 K T 3 = K T 4 = K ή = 51.2%] T1. The Initial pressure and temperature of the air taken through a Carnot cycle are 15 bar and 270 C resp ectively. F rom the init ial conditions, the air is expanded isothermally to three times its initial volume then the cycle is completed by isothermal compression and adiabatic comp ression. Take V 3 =6V 1. Determine 1) the pressure, volume and temperature at each corner of the cycle. 2) the thermal efficiency of the cycle 3) the work done per cycle. ANSWERS: a) V 1 = m 3 V 2 = m 3 V 3 = 0.63 m 3 V 4 = 0.21 m 3 T 1 = 543K T 2 = 543 K T 3 = K T 4 = K P 1 = 15 bar P 2 = 5 bar P 3 = 1.89 bar P 4 = 5.67 bar b) ή = 24.21% c) W.D =41.9 KJ] H1. A hot air engine works on Carnot cycle with thermal efficiency of 70%.if final temp of air is 20 ⁰C. Determine the initial temp. ANSWERS: [T 1 = o C] C2. An engine is work ing on ideal Otto cycle. The temp o f the beginning and the end ofcompression is 60 C and 450 C.Determine the air standard efficiency and compression ratio. ANSWERS: [r = 6.94 η = 53.92%] T2. In air standard Otto C ycle the Maximum and Minimum temperatures are 1673 K and 288K. The heat supplied per kg of air is 800 KJ. Calculate (i) The Compression Ratio. (ii) Efficiency (iii) Max & Min Pressures. Take C v = kj/kg K and γ = 1.4 for air. ANSWERS: [1) r=5.244, 2) η=48.46%] H2. Determine the Air Standard Efficiency of an Otto cycle from the Following Bore of the Cylinder is 14cm, Stroke Length 13 cm, Clearance Volume 290 cm 3 ANSWERS: [r = 7.9 η = 56.25%] C3. In an Otto cycle the co mpressio n ratio is 8. The temperatures at the beg inn ing of compression and at the end of heat supply are 3 10 K and 1600 K respectively. Assume γ=1.4 and C v = kj/kg K. F ind (i) Heat S upplied (ii) Efficiency of the cycle. ANSWERS: [1) Q = kj/kg, 2) η = 56.46%] T3. An engine works o n the constant vo lume cycle. It has a cylinder bore of 90 mm and p iston stroke of 100mm. the clearance vo lume of the engine is 0.06 litre. The actual thermal efficiency of the engine is 22%. Determine the relative efficiency o f the engine. Take γ=1.4.